Airflow sensor for a heat sink

ABSTRACT

An airflow sensor for a heat sink has a first portion having a first electrical point of contact, a second portion have a second electrical point of contact, and a deformable portion made of an electroactive material electrically coupled to the first and second portions. The deformable portion has first electrical properties measured between the first and second electrical points of contact when there is no airflow and the deformable portion is in a first position, and has second electrical properties different than the first electrical properties when a source of airflow blows air against the deformable portion, thereby causing the deformable portion to extend to a second position farther away from the source of airflow than the first position. The airflow sensor can be incorporated into a heat sink for an electronic component.

BACKGROUND

1. Technical Field

This disclosure generally relates to airflow sensors, and morespecifically relates to an airflow sensor for a heat sink.

2. Background Art

Heat sinks are commonly used in modern electronic systems to dissipateheat generated by electronic components, such as processors. A source ofair such as a fan is typically placed in proximity to a heat sink toproduce airflow over the heat sink, which enhances the ability of theheat sink to dissipate heat.

Modern heat sinks are typically modeled using thermal simulation.Prototypes are then built, which are qualified with thermal testvehicles and flow benches. However, even with thermal simulation andflow bench qualification, a heat sink may behave differently in a systemthan modeled. Oftentimes the internal environment is difficult topredict and model.

SUMMARY

An airflow sensor for a heat sink has a first portion having a firstelectrical point of contact, a second portion have a second electricalpoint of contact, and a deformable portion made of an electroactivematerial electrically coupled to the first and second portions. Thedeformable portion has first electrical properties measured between thefirst and second electrical points of contact when there is no airflowand the deformable portion is in a first position, and has secondelectrical properties different than the first electrical propertieswhen a source of airflow blows air against the deformable portion,thereby causing the deformable portion to extend to a second positionfarther away from the source of airflow than the first position. Theairflow sensor can be incorporated into a heat sink for an electroniccomponent.

The foregoing and other features and advantages will be apparent fromthe following more particular description, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING(S)

The disclosure will be described in conjunction with the appendeddrawings, where like designations denote like elements, and:

FIG. 1 is a side view of an airflow sensor;

FIG. 2 is an enlarged partial side view of the airflow sensor of FIG. 1showing how the deformable portion extends with airflow;

FIG. 3 is a side view of the airflow sensor of FIG. 1 mounted betweentwo fins on a heat sink;

FIGS. 4-7 show various possible configurations for the airflow sensor100 shown in FIGS. 1-3;

FIG. 8 is a flow diagram of a method for characterizing an airflowsensor;

FIG. 9 is a flow diagram of a method for logging information as anelectronic system runs;

FIG. 10 is a flow diagram of a method for determining airflow in anelectronic system using the airflow sensor;

FIG. 11 is a block diagram of an electronic system that includes a heatsink with an airflow sensor as described and claimed herein; and

FIG. 12 is a side view of the airflow sensor of FIG. 1 mounted to spanfour fins on a heat sink.

DETAILED DESCRIPTION

The disclosure and claims herein relate to an airflow sensor for a heatsink that has a first portion having a first electrical point ofcontact, a second portion have a second electrical point of contact, anda deformable portion made of an electroactive material electricallycoupled to the first and second portions. The deformable portion hasfirst electrical properties measured between the first and secondelectrical points of contact when there is no airflow and the deformableportion is in a first position, and has second electrical propertiesdifferent than the first electrical properties when a source of airflowblows air against the deformable portion, thereby causing the deformableportion to extend to a second position farther away from the source ofairflow than the first position. The airflow sensor can be incorporatedinto a heat sink for an electronic component.

Referring to FIG. 1, an airflow sensor 100 comprises a first portion110, a second portion 120, and a deformable portion 130 made of anelectroactive material having a first end connected to the first portion110 and a second end opposite the first end connected to the secondportion 120. The first portion 110 and second portion 120 are made of anelectrically conductive material. The first portion 110 includes acorresponding first electrical point of contact 140, and the secondportion 120 includes a corresponding second electrical point of contact142. In one suitable implementation, the first portion 110 and secondportion 120 are made of metal, and are connected to the deformableportion 130, which is made of an electroactive material. In anothersuitable implementation, the first portion 110, second portion 120, anddeformable portion 130 are all made from a single piece of electroactivematerial. Measuring resistance between the first and second electricalpoints of contact 140 and 142 results in a resistance reading thatvaries according to the degree to which the deformable portion 130 isextended due to airflow.

FIG. 1 includes a portion 150 that is shown enlarged in FIG. 2 todemonstrate the deformation of the deformable portion in the presence ofairflow. Deformable portion 130 is shown in a first position 130A in theabsence of airflow. For the specific configuration shown in FIG. 2, adistance d1 represents the position of the rightmost portion of thedeformable portion in position 130A from the points where the deformableportion 130 is connected to the first and second portions 110 and 120 inthe absence of airflow. In the presence of airflow, represented in FIGS.2 and 3 by arrow 210 in the direction shown, the deformable portion 130extends to a second position 130B farther away from the source of theairflow than the first position 130A, as shown by position 130B being adistance d2 that is farther in the direction of the airflow from thepoints where the deformable portion is connected to the first and secondportions 110 and 120 than when the deformable portion is in position130A. One can readily see from FIG. 2 that airflow extends thedeformable portion 130, and the deformation of the deformable portion130 can thus be used to detect airflow. While two positions 130A and130B are shown in FIG. 2, one skilled in the art will recognize thedeformable portion 130 may extend to a number of different positionsdepending on the speed of the airflow, which means the electricalproperties between the first and second contact points 140 and 142 cancharacterize the speed of airflow detected by the airflow sensor 100.

FIGS. 1 and 2 show side views of the airflow sensor 100, which does notindicate the width of the airflow sensor 100 that would be in contactwith the airflow 210. At one extreme, the airflow sensor 100 could havea cross-section with respect to the airflow 210 that is very small,meaning the airflow sensor 100 could have a width of a human hair orless. At the other extreme, the airflow sensor 100 could have across-section with respect to the airflow 210 that is significant,meaning the airflow sensor 100 substantially disrupts the airflow 210.In the most preferred implementation, the airflow sensor 100 has ageometry resembling a flat ribbon that is preferably more than amillimeter and less than ten millimeters wide. This flat ribbon geometryallows sufficient surface area for the airflow 210 to deform thedeformable portion 120 without significantly disrupting the airflow 210.In addition, thickness of the ribbon could be adjusted according toairflow ranges. Thus, a thicker ribbon could be used to provide areasonable deformation across the range of airflow when the expectedairflow is high. A thinner ribbon could be used when the expectedairflow is low. Using an appropriate specific design of airflow sensor100 allows measuring airflow without significantly disrupting theairflow.

The deformable portion 130 is preferably made from an electroactivematerial, such as one or more piezoelectric filaments or anelectroactive polymer. Electroactive materials are sometimes used in afirst mode of operation by applying an electrical signal such as avoltage across the electroactive material, which causes theelectroactive material to change shape. When the voltage is removed, theelectroactive material resumes its previous shape. Electroactivematerials can additionally be used in a second mode of operation wherethe shape is changed due to external forces, and the difference inelectrical properties between two contact points can be measured andrepresents the change in shape. The airflow sensor disclosed hereinoperates in the second mode of operation by allowing airflow to extendthe deformable portion, and the change in shape can be measuredaccording to changed electrical properties between the contact points.The deformable portion 130 thus serves as an elastic wind sock of sorts,extending according to the speed of the airflow, which allows measuringthe airflow by measuring the difference in electrical properties betweenthe contact points. In the most preferred implementation, extending thedeformable portion 130 due to airflow causes a change in electricalresistance between the contact point 140 and 142, which can be measuredand correlated to a speed of the airflow.

The airflow sensor 100 could be made from any suitable material orcombination of materials. In the most preferred implementation, thefirst portion 110, the second portion 120, and the deformable portion130 are all made of the same electroactive material. Suitableelectroactive materials include one or more piezoelectric filaments andan electroactive polymer. Of course, other electroactive materials couldalso be used. In an alternative implementation, the first portion 110and second portion 120 are made of metal, and are electrically coupledto the deformable portion 130, which is made of an electroactivematerial. Any suitable metal could be used for first and second portions110 and 120, including copper, nickel, indium or tin. Of course, alloysof different metals could also be used. In addition, non-metallicconductors or semiconductors could also be used. Any suitable materialsfor the airflow sensor 100 could be used as long as the deformableportion 130 deforms under the force of airflow, which causes electricalproperties between the contact points 140 and 142 that vary as afunction of speed of the airflow.

The airflow sensor 100 shown in FIGS. 1 and 2 can be used to measureairflow on a heat sink. Referring to FIG. 3, two fins 310 and 320 of aheatsink 300 are shown. Of course, the heat sink 300 could include otherfins not shown in FIG. 3. The airflow sensor 100 is placed between fins310 and 320 by bonding the first portion 110 to a lower surface of fin310 and by bonding the second portion 120 to the upper surface of fin320, as shown in FIG. 3. In one suitable implementation, either thefirst portion 110 could be electrically coupled to the fin 310 or thesecond portion 120 could be electrically coupled to the fin 320. In themost preferred implementation, both first portion 110 and second portion120 are electrically insulated from the fins 310 and 320. Bonding thefirst portion 110 and second portion 120 is a way to permanently attachthe airflow sensor 100 at a desired location on a heat sink. If atemporary attachment is needed, instead of bonding the first portion 110and second portion 120 to the fins of the heat sink, removablemechanical couplings such as clips or springs could be used so theairflow sensor 100 can be relocated to different positions on the heatsink as needed.

In the configuration shown in FIG. 3, the airflow sensor 100 willproduce different values of electrical resistance with different amountsof airflow between the first fin 310 and second fin 320. Because theairflow sensor 100 minimally disrupts the airflow, the airflow sensor100 provides crucial airflow information for a heat sink in an operatingenvironment in a manner that does not significantly negatively impactthe performance of the heat sink.

The placement of the airflow sensor 100 in FIG. 3 is shown on the rightedge of the heatsink. Note, however, the airflow sensor 100 could beplaced anywhere along the length of the heatsink 300 provided there isno obstruction to the airflow. Thus, airflow sensor 100 in FIG. 3 couldbe moved to the middle of heat sink 300 or to the left edge of heatsink300. The disclosure and claims herein extend to any suitable locationfor the airflow sensor 100 on a heat sink 300.

The airflow sensor could span multiple fins of a heat sink, as shown inFIG. 12. The airflow sensor 100 in FIG. 12 spans four fins 1210, 1220,1230 and 1240. The airflow sensor 100 can thus detect airflow flowingbetween these four fins. The disclosure and claims herein expresslyextend to any suitable location on a heatsink for the airflow sensor,whether spanning two fins or multiple fins.

The side view in FIG. 2 shows how the deformable portion 130 deformswithout knowing the width or shape of the deformable portion 130. FIGS.4-7 show various possible configurations for airflow sensor 100 shown inFIG. 2, and represent end views of different configurations in FIG. 2taken along the line 4-4. FIG. 4 shows a narrow ribbon configurationwhere the first portion 110, second portion 120 and deformable portion130 all have the same relatively narrow width. FIG. 5 shows a widerribbon configuration where the first portion 110, second portion 120 anddeformable portion 130 all have the same wider width. FIG. 6 shows aconfiguration where the first and second portions 120 have a relativelynarrow width, and the deformable portion 130 has narrow ends thatconnect to the first and second portions 110 and 120 with a wider centerthat has a larger cross-section for catching air, like a sail. FIG. 7shows a configuration where the first and second portions 110 and 120have a relatively narrow width, and the deformable portion 130 hasnarrow ends that connect to the first and second portions with a widercenter that includes multiple openings 610. Many other configurationsnot shown in FIGS. 4-7 could also be used, including multiple filamentsor strands, or any suitable shape or configuration that includes noholes or any suitable number of holes. The deformable portion 130 mayinclude any suitable configuration as long as the electrical propertiesmeasures between the contact points 140 and 142 vary according to thespeed of airflow.

While it is possible the airflow sensor 100 could be designed to provideresistance between the two electrical points 140 and 142 that islinearly proportional to airflow, other designs that do not provide suchlinear proportionality could also be used. In the most preferredimplementation, the airflow sensor is tested and characterized so itsperformance is known, and future readings can be compared to thecharacterization data to determine airflow. Referring to FIG. 8, method800 begins by attaching an airflow sensor to a heat sink (step 810),such as the configuration shown in FIG. 3. Next, the heat sink is placedon a flow bench, and a particular airflow is selected (step 820). Theselected airflow is then run over the heat sink (step 830). The airflowsensor reading is recorded for the known airflow (step 840). We assumesteps 820, 830 and 840 are repeated for several different airflows, sostep 850=NO, and these steps are repeated with a different selectedairflow. This characterization of airflow sensor readings to airflowcontinues until characterization of the airflow sensor is complete (step850=YES), at which point the airflow sensor readings are stored asairflow sensor characterization data (step 860). The airflow sensorcharacterization data stored in step 860 can then be used to determineairflow over the airflow sensor at any given point in time based on theelectrical resistance readings of the airflow sensor.

Electronic systems often log performance data. Referring to FIG. 9,method 900 monitors and logs performance data for an electronic system(step 910), and additionally logs the airflow sensor readings (step920). Logging airflow sensor readings at the same time other performanceparameters are logged provides data from which airflow can be determinedat particular points in time that correlate to the logged performancedata.

Referring to FIG. 10, a method 1000 begins by reading the loggedperformance data (step 1010). When airflow for the logged performancedata is not needed (step 1020=NO), method 1000 is done. For example, ifthe logged performance data is read in step 1010 to determine memoryutilization at a particular point in time, airflow will not affectmemory utilization, so the airflow information is not needed. Whenairflow for the logged performance data is needed (step 1020=YES), thelogged airflow sensor readings are read (step 1030), then converted toairflow using the airflow sensor characterization data (step 1040).Method 1000 thus provides logged performance data correlated withairflow, which allows determining whether airflow could have contributedto a logged event. For example, when a processor experiences a powerthrottling event, knowing the airflow at the time of the power throttlecould provide an indication of whether proper airflow was being appliedto the heat sink.

Referring to FIG. 11, an electronic system 1110 is shown, which includeselectronic components 1120. Electronic components 1120 can include anytype of electronic components, systems or subsystems, including withoutlimitation processors, memory, integrated circuits, discrete logic, harddisk drives, I/O adapters, etc. A performance measurement mechanism 1180monitors and logs data in a performance measurement log 1190. A heatsink 1130 is provided for one or more of the electronic components 1120that includes an airflow sensor 1140. Airflow sensor 100 shown in FIGS.1-3 is one suitable implementation for airflow sensor 1140 in FIG. 1.The airflow sensor 1140 is connected to an airflow sensor measurementmechanism 1150, which measures readings from the airflow sensor 1140. Inone suitable implementation, the readings could be electricalresistance. In another suitable implementation, the airflow sensormeasurement mechanism 1150 could measure a voltage across the airflowsensor 1140. When steps are taken to characterize an airflow sensor asshown in method 800 in FIG. 8, the airflow sensor characterization datastored in step 860 is represented as 1160 in FIG. 11. An airflow sensormeasurement log 1170 preferably includes airflow sensor measurementsover time. In the most preferred implementation, both the performancemeasurement log 1190 and airflow sensor measurement log 1170 havetimestamped entries that allow correlating the two. Thus, if theperformance measurement mechanism 1180 determines processor temperaturerose at a given point in time, the airflow sensor measurement log 1170can be consulted to determine the airflow through the processor'sheatsink at the same point in time. Correlating airflow to logged systemevents thus provides a way to determine whether airflow was acontributing factor in the logged system events.

Many variations are possible within the scope of the disclosure andclaims herein. For example, while a single airflow sensor on a singleheatsink is shown in FIG. 3, multiple airflow sensors could be used on asingle heatsink, and a single airflow sensor could be used between twoadjacent heatsinks. The use of multiple airflow sensors in differentregions of a heatsink could be very helpful in testing andcharacterizing performance of a heat sink. In addition, multiple airflowsensors that have different properties could be used together. Forexample, three airflow sensors could be used on a heat sink, with afirst airflow sensor that measures airflow up to a first threshold, asecond airflow sensor that measures airflow from the first threshold toa second threshold, and the third airflow sensor that measure airflowfrom the second threshold to a third threshold. The disclosure andclaims herein expressly extend to any suitable number of airflow sensorsin any suitable configuration for measuring airflow on one or more heatsinks.

An airflow sensor for a heat sink has a first portion having a firstelectrical point of contact, a second portion have a second electricalpoint of contact, and a deformable portion made of an electroactivematerial electrically coupled to the first and second portions. Thedeformable portion has first electrical properties measured between thefirst and second electrical points of contact when there is no airflowand the deformable portion is in a first position, and has secondelectrical properties different than the first electrical propertieswhen a source of airflow blows air against the deformable portion,thereby causing the deformable portion to extend to a second positionfarther away from the source of airflow than the first position. Theairflow sensor can be incorporated into a heat sink for an electroniccomponent.

One skilled in the art will appreciate that many variations are possiblewithin the scope of the claims. Thus, while the disclosure isparticularly shown and described above, it will be understood by thoseskilled in the art that these and other changes in form and details maybe made therein without departing from the spirit and scope of theclaims.

1. An airflow sensor comprising: a first portion having a firstelectrical point of contact; a second portion have a second electricalpoint of contact; and a deformable portion made of an electroactivematerial, the deformable portion having a first end electrically coupledto the first portion and a second end opposite the first endelectrically coupled to the second portion, wherein the deformableportion has first electrical properties measured between the first andsecond electrical points of contact when there is no airflow and thedeformable portion is in a first position, and has second electricalproperties measured between the first and second electrical points ofcontact different than the first electrical properties when a source ofairflow blows air against the deformable portion, thereby causing thedeformable portion to extend to a second position farther away from thesource of airflow than the first position.
 2. The airflow sensor ofclaim 1 wherein electrical resistance between the first and secondelectrical points of contact is a function of airflow through theairflow sensor.
 3. The airflow sensor of claim 1 wherein voltage betweenthe first and second electrical points of contact is a function ofairflow through the airflow sensor.
 4. The airflow sensor of claim 1wherein the first and second portions are made of the same electricallyconductive material.
 5. The airflow sensor of claim 4 wherein theelectrically conductive material comprises metal.
 6. The airflow sensorof claim 1 wherein the first and second portions are made of the sameelectroactive material as the deformable portion.
 7. The airflow sensorof claim 1 wherein the first and second portions and the deformableportion are made from a single piece of electroactive material.
 8. Theairflow sensor of claim 1 wherein the electroactive material comprisesat least one piezoelectric filament.
 9. The airflow sensor of claim 1wherein the electroactive material comprises an electroactive polymer.10. A heat sink comprising: a first thermally-conductive fin; a secondthermally-conductive fin substantially parallel to and underlying thefirst thermally-conductive fin and thermally coupled to the firstthermally-conductive fin; and an airflow sensor comprising: anelectrically conductive upper portion coupled to a bottom surface of thefirst thermally-conductive fin, the upper portion comprising a firstelectrical point of contact; an electrically conductive lower portioncoupled to a top surface of the second thermally-conductive fin, thelower portion comprising a second electrical point of contact; and adeformable portion made of an electroactive material, the deformableportion having a first end electrically coupled to the upper portion anda second end opposite the first end electrically coupled to the lowerportion, wherein the deformable portion has first electrical propertiesmeasured between the first and second electrical points of contact whenthere is no airflow and the deformable portion is in a first position,and has second electrical properties different than the first electricalproperties when a source of airflow blows air against the deformableportion, thereby causing the deformable portion to extend to a secondposition farther away from the source of airflow than the firstposition.
 11. The heat sink of claim 10 wherein electrical resistancebetween the first and second electrical points of contact is a functionof airflow through the airflow sensor.
 12. The heat sink of claim 10wherein voltage between the first and second electrical points ofcontact is a function of airflow through the airflow sensor.
 13. Theheat sink of claim 10 wherein the first and second portions are made ofthe same electrically conductive material.
 14. The heat sink of claim 13wherein the electrically conductive material comprises metal.
 15. Theheat sink of claim 10 wherein the first and second portions are made ofthe same electroactive material as the deformable portion.
 16. The heatsink of claim 10 wherein the first and second portions and thedeformable portion are made from a single piece of electroactivematerial.
 17. The heat sink of claim 10 wherein the electroactivematerial comprises at least one piezoelectric filament.
 18. The heatsink of claim 10 wherein the electroactive material comprises anelectroactive polymer.
 19. A method for determining airflow through aheat sink in an electronic system, the method comprising: (A) providinga heat sink for an electronic component, the heat sink comprising: afirst thermally-conductive fin; a second thermally-conductive finsubstantially parallel to and underlying the first thermally-conductivefin and thermally coupled to the first thermally-conductive fin; anairflow sensor comprising: an electrically conductive upper portioncoupled to a bottom surface of the first thermally-conductive fin, theupper portion comprising a first electrical point of contact; anelectrically conductive lower portion coupled to a top surface of thesecond thermally-conductive fin, the lower portion comprising a secondelectrical point of contact; and a deformable portion made of anelectroactive material, the deformable portion having a first endelectrically coupled to the upper portion and a second end opposite thefirst end electrically coupled to the lower portion, wherein thedeformable portion has first electrical properties measured between thefirst and second electrical points of contact when there is no airflowand the deformable portion is in a first position, and has secondelectrical properties different than the first electrical propertieswhen a source of airflow blows air against the deformable portion,thereby causing the deformable portion to extend to a second positionfarther away from the source of airflow than the first position; (B)selecting an airflow; (C) running the selected airflow over the heatsink; (D) measuring electrical resistance between the first and secondelectrical points of contact; (E) recording the measured electricalresistance as correlating to the selected airflow; (F) repeating steps(B) through (E) for a plurality of airflows; (G) storing the measuredelectrical resistance for the plurality of airflows as airflow sensorcharacterization data; (H) monitoring and logging performance of theelectronic system; (I) monitoring and logging readings of the airflowsensor corresponding to the logged performance of the electronic system;and (J) converting the logged readings of the airflow sensor to airflowsusing the airflow sensor characterization data.